U.S. patent number 4,481,384 [Application Number 06/285,654] was granted by the patent office on 1984-11-06 for voice recognizing telephone call denial system.
This patent grant is currently assigned to Mitel Corporation. Invention is credited to Terrence H. Matthews.
United States Patent |
4,481,384 |
Matthews |
November 6, 1984 |
**Please see images for:
( Certificate of Correction ) ** |
Voice recognizing telephone call denial system
Abstract
A call denial apparatus for denying a subscriber's access to a
trunk. A voice recognizer is connected to the trunk, and receives a
password spoken by the subscriber. The apparatus then receives
digits dialed by the subscriber over the subscriber's line and
carried by the trunk, matching them with one or a series of digits
stored in a memory. In the event the password or subscriber's voice
matches a predetermined password or voice, the digits which are
dialed are passed over the trunk. However in the event that the
password or voice does not match the predetermined password or
voice, and in the event a predetermined one or group of digits are
dialed which match a prohibited digit or group of digits stored in
the memory, the trunk is split, and the subscriber is restricted
from further access to the trunk. Thus only predetermined
subscribers have full access to the trunk, and other subscribers
have access only for limited services, or for no services. The
voice recognition design allows different subscribers to have
different classes of service, and for the first time does not tie
trunk restriction to a subscriber's line, but to an actual
subscriber.
Inventors: |
Matthews; Terrence H. (Kanata,
CA) |
Assignee: |
Mitel Corporation (Kanata,
CA)
|
Family
ID: |
4119763 |
Appl.
No.: |
06/285,654 |
Filed: |
July 21, 1981 |
Foreign Application Priority Data
Current U.S.
Class: |
379/188; 379/198;
379/903 |
Current CPC
Class: |
H04M
1/66 (20130101); Y10S 379/903 (20130101) |
Current International
Class: |
H04M
1/66 (20060101); H04M 001/66 () |
Field of
Search: |
;179/18DA,18D,18B,18BE,18FH ;381/42 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Brown; Thomas W.
Attorney, Agent or Firm: Levine; Alan H.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A trunk splitting circuit comprising:
(a) means for detecting seizure of a trunk,
(b) means for recognizing a predetermined enunciated word audio
signal carried by the trunk following detection of said
seizure,
(c) means for detecting dialed digits carried by the trunk
following said enunciated word signal,
(d) means for storing representations of one or a plurality of
predetermined digits, and for comparing said predetermined digit or
digits with the dialed digits, and
(e) means for splitting said trunk in the event of both the
matching of said predetermined digit or digits with said dialed
digits and the recognition of audio signals other than said
predetermined audio signal.
2. A trunk splitting circuit as defined in claim 1, including means
for generating a data signal corresponding to the predetermined
audio signal as a class of service indicator signal, means for
correlating the class of service indicator data signal with said
representations of predetermined digits, and means for enabling the
trunk splitting means in the event the class of service signal does
not correlate with said representations of predetermined
digits.
3. A trunk splitting circuit as defined in claim 1 or 2, in which
the data signal generating means is comprised of a speech
recognition circuit adapted to distinguish at least one
predetermined word as said predetermined audio signal, and to
generate said data signal in response to the distinguishing of said
word.
4. A trunk splitting circuit as defined in claim 2, in which the
data signal generating means is comprised of a speech recognition
circuit adapted to distinguish at least one predetermined voice
pattern as said predetermined audio signal, and to generate said
data signal in response to the distinguishing of said word.
5. A trunk splitting circuit as defined in claim 2, in which the
data signal generating means is comprised of a speech recognition
circuit adapted to distinguish predetermined voice patterns as said
predetermined audio signal, and to generate data signals in
response to said voice patterns as class of service indicator data
signals, and means for enabling the trunk splitting means in the
event predetermined class of service indicator signals do not
correlate with predetermined ones or groups of dialed digits.
6. A call denial apparatus for use in a telephone system
comprising:
(a) means for detecting seizure of a trunk,
(b) means for splitting and terminating the trunk upon detection of
the trunk seizure, into an originating portion and a central office
portion, and for terminating the central office portion so as to
maintain it in a seized condition,
(c) voice recognizing means for detecting a predetermined voice
pattern carried by the originating portion of the trunk when the
trunk is split, and for generating a predetermined class of service
data signal in response thereto,
(d) means for reconnecting said portions of the trunk upon
generation of said data signal,
(e) a dialed digit signal detector connected to the trunk,
including means for registering one or a sequence of dialed
digits,
(f) means for storing one or a sequence of representations of
predetermined digits, and for comparing them with said dialed
digits, and
(g) means for splitting the central office portion from the
originating portion of the trunk in the event of both generation of
a class of service data signal other than said predetermined class
of service data signal and matching of said dialed digits with said
one or a sequence of said predetermined digits, whereby further
access to the central office portion of the trunk from the
originating portion is denied and whereby the trunk is maintained
connected in the event of either said predetermined class of
service data signal being generated or the detected digits being
other than said one or predetermined sequence of digits, thus
allowing said digit signals to be transmitted via the central
office portion of the trunk.
7. A call denial apparatus as defined in claim 6, in which the
means for detecting seizure of a trunk includes a line current
detector.
8. Apparatus as defined in claim 7 further including means for
detecting digits dialed from the originating portion of the trunk,
means for storing a predetermined digit or series of digits, means
for comparing the detected digits with said stored digit or series
of digits, and means for retaining the trunk continuous in the
event of both the generation of predetermined form of the first
data signal and the coincidence of the dialled digits and said
stored digit or series of digits, whereby further progress of the
call is facilitated, and for splitting the trunk in the event of
generation of other forms of the first data signal and the
coincidence of the dialled digits and said stored digit or series
of digits, whereby further progress of the call is denied.
9. A call denial apparatus for use in a telephone system having a
plurality of subscribers' lines interconnectable with at least one
trunk comprising:
(a) means for detecting seizure of a trunk,
(b) means for connecting a voice recognition circuit to the trunk
upon detection of said seizure,
(c) means for detecting a predetermined voice signal received from
a subscriber's line which has access to the trunk,
(d) means for storing a representation of at least one
predetermined digit,
(e) means for registering at least one digit dialed over the trunk,
and for comparing it with said predetermined digit, and
(f) means for open circuiting the trunk in the event of both the
detection of voice signals other than the predetermined voice
signal and the matching of said dialed digit with said
predetermined digit, whereby the subscriber's line is restricted
from further access to the trunk.
10. A call denial apparatus as defined in claim 9, in which the
means for registering at least one digit dialed over the trunk
includes a digit receiver and means for storing representations of
a plurality of received digits received by said receiver, and
further including means for storing representations of
predetermined digits, and means for enabling the trunk open
circuiting means upon one or a sequence of representations of the
received digits matching one or a sequence of the representations
of said predetermined digits.
11. A trunk splitting circuit comprising:
(a) means for detecting seizure of a trunk,
(b) means for splitting the trunk upon detection of said seizure
into a subscriber portion and a central office portion,
(c) means for connecting a voice or password recognizing circuit to
the subscriber portion of the trunk upon the trunk being split,
(d) means for detecting a predetermined password or voice received
from the subscriber portion of the trunk,
(e) means for storing a representation of at least one
predetermined digit,
(f) means for registering at least one digit dialed over the
subscriber portion of the trunk, and for comparing it with said
predetermined digit, and
(g) means for maintaining the trunk split in the event of both the
detection of passwords or voices other than the predetermined
password or voice and the matching of said dialed digit with said
predetermined digit.
12. A method of denying a subscriber's line out of a group of
subscribers' lines use of a trunk comprising:
(a) detecting seizure of the trunk,
(b) applying a voice recognition circuit to the trunk upon
detection of its seizure,
(c) providing for detection of a predetermined voice signal that
may be received from the subscriber's line,
(d) monitoring the trunk for the presence of destination code digit
signals,
(e) comparing said destination code digit signals with one or a
plurality of predetermined destination code digit signals, and
(f) splitting the trunk in the event of the detection of voice
signals other than the predetermined voice signal and
correspondence of the destination code digit signals with said
predetermined one or plurality of signals, whereby further access
to the trunk by the subscriber's line is inhibited.
13. A method of denying a subscriber use of a communication toll
facility comprising:
(a) detecting seizure of the communication toll facility,
(b) monitoring a transmission path associated with said signal
facility with a voice recognizing circuit,
(c) detecting a predetermined voice or spoken password carried by
the transmission path,
(d) monitoring the transmission path for the presence of
destination code signals,
(e) comparing said destination code signals with one or a plurality
of predetermined destination code signals, and
(f) disconnecting the communication toll facility from utilization
by the subscriber in the event of detection of voices or spoken
passwords other than the predetermined voice or spoken password and
correspondence of the destination code signals with said one or a
plurality of signals, or
(g) maintaining said facility seized and utilizable by the
subscriber in the event of detection of said predetermined voice or
spoken password by the voice recognizing circuit and correspondence
of the destination code signals with said one or a plurality of
signals.
14. A method as defined in claim 13, in which the communication
toll facility is a trunk which includes said transmission path.
15. A method of denying a subscriber use of a communication
facility comprising:
(a) detecting seizure of the communication facility,
(b) monitoring a transmission path associated with said facility
with a voice recognizing circuit,
(c) detecting a predetermined voice or spoken password received
from the transmission path,
(d) monitoring the transmission path for the presence of
destination code signals,
(e) comparing said destination code signals with one or a plurality
of predetermined destination code signals, and
(f) disconnecting the communication toll facility from utilization
by the subscriber in the event of detection of voices or spoken
passwords other than the predetermined voice or spoken password,
or
(g) maintaining said facility seized and utilizable by the
subscriber in the event of detection of said predetermined voice or
spoken password by the voice recognizing circuit and correspondence
of the destination code signals with said one or a plurality of
signals.
16. A method as defined in claim 15 in which the communication
facility is a voice or data trunk which includes said transmission
path.
Description
This invention relates to call restriction apparatus for telephone
systems, and particularly to such apparatus which can be used in
conjunction with a trunk, but is personal to the subscriber, and
not to his telephone set.
It is often desirable to restrict certain personel from making
unauthorized toll calls, or from gaining access to certain
trunk-interfaced facilities. Yet at the same time it is desirable
to give these and other subscribers access to trunks leading to a
central office for local calls. Toll or other trunk restriction
apparatus has previously determined whether a call should be
restricted or not based on the detection of particular digits
dialed at certain telephone sets, or upon recognition of
predetermined numbers or specific digits dialed, to terminate
further processing of the call. However this apparatus could not
distinguish whether the subscriber is or is not authorized to make
the call. An unauthorized subscriber could gain access to
subscriber's sets to which trunk access is given.
In U.S. Pat. No. 4,000,380 issued Dec. 28, 1976, invented by J. M.
Jackson, an apparatus is described which utilizes a circuit
interconnected with the internal circuitry of each telephone set
which is to be restricted. The apparatus counts the number of
digits and upon counting a predetermined number of digits (which is
evidence of a toll or outgoing call), prevents the transmission of
additional digits. Since each restricted telephone set must be
modified, extraordinary care must be taken before station sets are
interchanged between employees, and special record keeping is
required to keep track of the station sets. Both standard and
non-standard telephone sets must also be manufactured and stocked.
This system also does not distinguish between destinations of calls
allowed or restricted from a particular telephone set, or which
subscriber is using the telephone set, since only the number of
digits are counted. Clearly this system introduces substantially
increased costs and has minimal flexibility.
Another call denial circuit is described in U.S. Pat. No.
3,996,425, issued Dec. 7, 1976, to A. E. Low and M. J. Sturtevant.
This system is used in association with a PABX and utilizes a
common check circuit and a plurality of digit registers which are
individually associated with particular lines to record calling
data. The invention is directed to means for providing a
multifrequency facility to circuitry which could previously detect
rotary dialled digits. However a circuit must still be used
associated with each line connected to the PABX. Further the system
must be interconnected with a particular type of PABX, since it
interacts with the PABX common control. Intimate knowledge of the
PABX circuitry must therefore be available in order to implement
that system. The system also allows unauthorized persons to gain
access to trunks from which they are restricted, since it cannot
distinguish between authorized and unauthorized persons.
Canadian patent application No. 359,108, filed Aug. 27, 1980,
issued as Pat. No. 1,155,207, and corresponding U.S. Pat. No.
4,355,208, assigned to Mitel Corporation, describe a denial circuit
which can be used with a PABX of unknown design, or with any
switching network in which a plurality of lines have access to a
plurality of trunks. That circuit is connected only to the trunks
and to the lines, and not to the telephone sets. The number of
circuits required are related to the number of trunks, rather than
the number of lines, which substantially decreases the amount and
complexity of the equipment, since the number of trunks provided is
smaller than the number of lines. However, this circuit still
restricts the use of trunks switched to or from particular
telephone sets, and does not restrict individual subscribers.
There are three problems of interest associated with call
restriction: (a) determination of which subscriber is making the
call, (b) determination of what trunk is utilized, and (c)
determination of the destination of the call, as by the dialled
digits, whereby restriction can be effected. Preferably a class of
restriction service should be related to the subscriber, himself,
and not to the telephone set or line which he uses.
In U.S. Pat. No. 4,000,380, the problems of identifying the station
set and the outgoing trunk are solved by associating the
restriction apparatus with each telephone set. A rudimentary
identification of a restricted number is made by counting the
number of digits dialled.
In U.S. Pat. No. 3,996,425, the identity of the restricted
telephone set and outgoing trunk are established by the PABX
itself. A special memory associated with the PABX identifies
restricted numbers.
In Canadian patent application Ser. No. 359,108, the trunk or
destination path, and the station set having access thereto is
identified using a tracer signal. Identity of the restricted number
can then be performed by known methods such as by storing a
restricted digit or series of digits in a microprocessor memory,
comparing a dialled digit or digits with the restricted number, and
if a match is found, dropping the trunk in the event than an
acceptable station set has not been identified.
According to the present invention, once the subscriber gains
access to the central office trunk, as by dialing "9" in a PABX,
the central office portion of the trunk is terminated in the
present circuit and the PABX portion is temporarily split and
connected to a speech recognition circuit. The subscriber then
speaks into his telephone handset, giving a password, his name, or
another predetermined word. The speech recognition circuit
translates the enunciated word into data bits which are applied to
a data bus, to which a control microprocessor is connected.
The speech recognition circuit indeed can be arranged in one of a
number of ways, depending on the desire of the designer. In one
arrangement, a predetermined data word is applied to the bus only
if the speech recognition circuit recognizes the word which is
received. In another arrangement the speech recognition circuit
outputs a predetermined data word which corresponds to recognition
both of the voice of the subscriber and to the spoken word, or,
alternatively, upon the recognition only the voice of the calling
subscriber. In another arrangement, the speech recognition circuit
outputs a data word corresponding to whatever enunciated word it
recognizes is applied to the data bus, and the recognition of a
restricted or allowed subscriber is performed by the microprocessor
comparing the data word with a look-up table of predetermined data
words corresponding to the voice of a subscriber or a password.
If the voice or password is not recognized, or is recognized but
the look-up table specifies a partly restrictive class of service,
the temporary split is closed, and dial tone from the central
office is returned to the calling subscriber. The subscriber dials
his digits. A digit receiver translates the digits to the central
microprocessor which compares the digits with a further look-up
table. If a toll call, for example, has been dialed a predetermined
sequence of digits is recognized, and the trunk is permanently
split (until the subscriber hangs up). If desired, the PABX portion
of the trunk can be connected to a warning tone trunk. If a local
call is dialed, the trunk may not be split.
If the voice or password is recognized, after the calling
subscriber dials his digits, the trunk is maintained continuous,
and the call is put through.
As an alternative, the trunk can be split and reconnected only if
the voice or password of the subscriber is recognized, then
allowing all dialed digits to be passed through to the central
office.
Since the calling subscriber can call on any telephone set, access
or denial of the trunk is personalized to the subscriber himself.
Special circuitry need not be associated with the telephone set,
allowing the freedom to utilize any telephone set by any
subscriber. Neither the telephone sets, nor the line terminations
on the PABX need be modified, but only the much smaller numbers of
trunks to be restricted which are connected to the PABX. The PABX
user thus has substantially increased flexibility of use, and
interchangeability of telephone sets.
The invention in general is a trunk splitting circuit for use in a
call denial apparatus comprising a circuit for detecting seizure of
a trunk, a speech recognizing circuit for recognizing a
predetermined enunciated word signal carried by the trunk following
the seizure, a circuit for detecting dialed digits carried by the
trunk following the enunciated word signal, and a circuit for
splitting the trunk in the event of both the detection of
predetermined ones of the dialed digits and the absence of
recognition of the predetermined audio signal.
The invention is also a method of denying a subscriber's line out
of a group of subscribers' lines which have access to a trunk
comprising the steps of detecting seizure of the trunk, applying a
voice recognition circuit to the trunk upon detecting of its
seizure, detecting a predetermined voice signal received from the
subscriber's line, disconnecting the voice recognition circuit from
the trunk upon detection of any voice signal from the subscriber's
line, monitoring the trunk for the presence of destination code
digits, and splitting the trunk in the event of no detection of the
predetermined voice signals and of matching of the destination code
digits with a predetermined one or plurality of digits, whereby
further access to the trunk by the subscriber's line is
inhibited.
It should be noted that while the present circuit is described in
terms of a call denial system, it can also be used to facilitate
access to or denial of special service circuits, using similar
principles. The circuit has particular utility in unlocking
toll-based service circuits. Thus, using the present circuit, every
subscriber accessing a PABX, or other switching machine, or trunks
can be denied long distance service unless the subscriber's voice
is recognized, or can be denied being given access on the same
basis to networks, conferencing circuits, etc. Since a voice
recognition distinguishes between central subscribers, different
classes of service can be provided to different subscribers.
A better understanding of the invention will be obtained by
reference to the detailed description below, and to the following
drawings, in which:
FIG. 1 is a block schematic of the preferred embodiment of the
invention,
FIGS. 2a, 2b, and 3 are schematic diagrams of the block portions of
the invention shown in FIG. 1, and
FIG. 2c which appears on the same page as FIG. 2b depicts how FIGS.
2a and 2b are to be placed together to form a complete schematic
diagram.
The following description is of an apparatus which includes both
the invention and ancilliary circuits, and utilizes a
microprocessor. The function of the microprocessor and of the
present invention is described in sufficient detail to allow a
person skilled in the art to prepare an operation program. However
as neither the microprocessor itself nor its program are the
subject of this invention, and since the principles of the
microprocessor and its programming are well known, a detailed
description thereof is believed to be redundant to a person seeking
an understanding of the present invention and will not be
detailed.
Turning first to FIG. 1, which is a block schematic of the
invention, the PABX 1 to which the invention is be connected which
can be of standard and known construction, such as type SX-200.TM.,
sold by Mitel Corporation of Kanata, Canada. The PABX has at least
one trunk 2, and a plurality of subscriber lines T,R connected
thereto. The PABX interconnects any of the subscribers lines one to
another, or to one or another of the trunks. The trunk shown
connects to a central office C.O. but can alternatively be
connected to a special service circuit such as a conferencing
circuit, etc.
A pair of line current detectors 16 are connected to the trunk 2,
and are adapted to detect seizure of the trunk. Upon detection of
the seizure, they apply a binary data signal to a data bus 4. Data
bus 4 is accessed by microprocessor 5 and memory 6.
Upon the microprocessor recognizing that the trunk has been seized,
it applies a signal to data bus 4 which is decoded in decoder 10,
and which causes the operation of relay A.
Relay A, in closing, causes operation of transfer contacts A.sub.1
and A.sub.2. This splits the trunk into an originating portion
connected to the PABX and a central office portion which leads to
the central office.
The originating portion of the trunk is connected via contacts
A.sub.1 and A.sub.2 to the input of amplifier 7, the output of
which is connected to the input of a speech recognition circuit 8.
This circuit analyzes input voice signals, and in response to an
algorithm contained therein, applies corresponding data signals to
bus 4. The microprocessor 5 in conjunction with its memory 6,
compares the data signals which are applied from speech recognition
circuit 8 with previously stored data signals which correspond to
predetermined subscriber's voices or words.
The data signals can be stored by dialing a predetermined secret
access code, following which the subscriber enunciates the password
after the access code is dialed (recognized by an m.f. receiver to
be described below), the voice recognition circuit is reconnected
to the trunk, and the data signals corresponding to the voice or
password passed to the data bus for storage in the memory under
control of the microprocessor.
Returning now to the circuit in the splitting mode, in one
embodiment, if a match is made, it applies binary signals to data
bus 4 to release relay A, reestablishing the connection of the
trunk from the PABX to the central office. However if no match is
found, the switches A.sub.1 and A.sub.2 remain operated, with the
trunk split, thus denying the subscriber use of the trunk. A
current detector 16 detects when the subscriber's line has returned
to an on-hook condition, and applies signals to bus 4, thus
advising the microprocessor that the split nature of the trunk can
be restored to continuity.
Assuming that the voice is recognized and the trunk is cut through
to the central office, dial tone is returned to the trunk, which is
heard by the subscriber. The subscriber can then dial the outgoing
call.
Just prior to splitting the trunk, the microprocessor also applies
a data word to decoder 10 which causes operation of trunk hold
circuit 13. This circuit closes a switch in series with a resistor
across the central office portion of the trunk, of value about 300
ohms, to load and hold the trunk to the central office. When the A
relay is released, reclosing the trunk, the hold circuit 13 is also
released, unloading the trunk.
According to a second, and preferred embodiment, if voice or
password recognition is made, one type of indication signal is
stored in the microprocessor memory. Digits which are then dialed
by the subscriber are ignored by the present circuit, allowing them
all to pass to the central office. Alternatively, the present
circuit can monitor the dialed digits, storing an indication signal
corresponding to the voice or password, and reacting to split the
trunk if the recognized voice or password indicates a particular
class of service.
If the voice or password recognition is not made, the present
circuit monitors subsequent dialed digits, and if predetermined
ones or sequences of numbers are dialed, reacts to split the trunk
as described below.
A multifrequency tone signalling receiver 14 has its inputs
connected to the originating portion of the trunk. The subscriber
m.f. dials in the desired destination number, which is transmitted
via the trunk to the central office and is also detected in
receiver 14. The outputs of receiver 14 are connected to the inputs
of a decoder 15, which generates a binary signal corresponding to
the keyed digits and applies it to data bus 4.
Should the subscriber's set utilize dial pulses these are detected
by current detector 16 and line voltage detector 3, connected to
trunk 2. The current detector 16 is comprised of low resistance
(such as 39 ohms) resistors connected in series with the trunk. A
transistor circuit detects voltage changes across the resistors,
and generates corresponding binary signals which are applied to
data bus 4. A suitable circuit for the dial pulse detector 16 is
described in Canadian patent application Ser. No. 342,522 filed
Dec. 21, 1979, entitled DIAL PULSE DETECTION CIRCUIT invented by
Brian PASCAS and Brian VAUGHAN. Dial pulse detectors are well
known, and any one which can apply suitable signals to the
microprocessor can be used.
The resulting keyed or dialled digits are received by
microprocessor 5, which compares the digits with a look-up table in
memory 6. If the dialled digits correspond to a predetermined
forbidden number or sequence stored in memory 6, microprocessor 5
applies a binary signal to data bus 4, which is decoded in decoder
10, which operates relay B. Relay B splits the trunk by opening
contacts B.sub.1 in series therewith, which denies further access
of the subscriber to the central office portion of the trunk. At
the same time the central office portion of the trunk to the
central office is released.
Distinctive classes of service can thus be provided for different
subscribers, since recognition of their voices allows
distinguishing between each. Denial of use of the trunk thus can be
considered as one of the classes of service. Other classes can be
denial or provision of a conference trunk, WATS services, etc.
As a further feature, the design can have microprocessor 5 operate
relay B to transfer contacts which connects the subscriber's
portion of the trunk to an oscillator, and also a switch within the
oscillator which causes generation of a tone frequency (diversion
tone) which is heard by the subscriber and indicates to him that a
forbidden sequence of numbers has been dialed, and that further
processing of the call has been terminated.
Relay B, rather than operating break contact B.sub.1 in series with
the trunk, can instead operate a pair of transfer contacts which
both breaks the trunk and transfers the originating portion to a
diversion trunk, which can carry a recorded message, a tone, or the
like.
It may be recognized that relays A and B both act to split the
trunk, which would appear to make relay B redundant. However it is
preferred that two such relays should be used since amplifier 7 and
speech recognition circuit 8 can be shared by a plurality of
trunks. Relay contacts similar to the A.sub.1 contacts connected to
other A relays are in this case connected to the input of amplifier
7. Relay A therefore should preferably remain operated only during
the voice detection period, and it is preferred that an additional
B relay which can remain operated for relatively long periods of
time should be used for the actual denial trunk split function.
Since no modification to the station set or to the subscriber line
inputs to the PABX need be made, great flexibility and ease of
interchangeability of the denial feature between station sets are
thus afforded.
The output of the speech recognition circuit thus effectively
becomes a class of service indicator. Since the look-up table in
memory 6 can store as many digits as desired, the circuit can
provide a denial on either one or a sequence of predetermined
dialled digits, which can be easily changed and made individual to
each subscriber personally.
During normal operation of the trunk, ringing current can of course
appear on the trunk from the central office which is directed to
the PABX. A ringing current or voltage detector 17 is also
connected across the trunk, and provides a binary signal to data
bus 4 for reception by microprocessor 5 upon detection of ringing.
Upon detection of ringing, and seizure of the trunk, the
microprocessor is inhibited upon receipt of the noted binary signal
from causing operation of relays A or B which would otherwise split
the trunk for this incoming type of call.
As an additional feature a polarity detector 18 can be connected
across the trunk, which detects seizure by polarity reversal. When
the trunk has first been split by relay A, it is held seized to the
central office by operation of hold circuit 13. At the same time
the microprocessor causes operation of relay C by applying a word
to data bus 4 which is decoded in decoder 10. The contacts of relay
C are located in the trunk hold circuit 13, and provide a battery
polarity reversal in a well known manner.
The look-up table in memory 6 can be established by the use of a
key pad 19, interfacing with binary encoder 20 which has its output
connected to data bus 4. A binary decoder 21 has its inputs
connected to data bus 4, and its outputs to a digital display 22.
Programming of the microprocessor utilizing a key pad and encoder,
and displaying the data words applied thereto using a decoder and
display are well known, and further explanation would be redundant
to a person skilled in the art.
Turning now to FIGS. 2, 3 and 4, the invention is shown in more
detail. FIG. 2 shows how FIGS. 2a and 2b are to be joined to make a
single schematic. It is assumed that a person skilled in the art
has sufficient knowledge of microprocessor circuitry techniques and
programming sufficient to be able to drive the circuit described
below. It is preferred that the microprocessor should be type 6802,
available from MOTOROLA, INC. of the United States, and memory 6
should be appropriate interfacing ROMs and RAMs. A full description
of the operation of such circuitry is available from Motorola Inc.,
and also may be found in the publication MICROCOMPUTER PRIMER by M.
Waite and M. Pardee, published by Howard M. Sams & Co., Inc. of
Indianapolis, Ind., U.S.A.
In the figures described below, it is assumed that the system
utilizes an eight parallel bit data bus, labelled D0-D7. While the
data bus leads are shown, the address bus, clock source, power
supply, enable leads, etc., are not shown, since their structure
are believed to be within the normal skill of the microprocessor
designer.
The trunk leads 2 connected to PABX 1 (FIG. 1) labelled PT and PR
are connected through a dial pulse detection circuit 30 to trunk
splitting transfer contacts 31A and 31B. These contacts are part of
a relay which also includes relay coil 31C (see block 65). The
output of the dial pulse detection circuit is connected via buffers
32A and 32B to data bus leads D0 and D1 respectively.
The dial pulse detection circuit 30 can be any well known circuit,
or the one which is described in the aforenoted patent application
describing the invention DIAL PULSE DETECTION CIRCUIT, invented by
Brian PASCAS and Brian VAUGHAN.
The break contacts of the relay contacts 31A and 31B are normally
closed, connecting the PABX portion through to the central office
portion of the trunk. The make contact portions are connected on
the tip side of the trunk via resistor 32 to ground, and on the
ring side via resistor 33 to a source of potential -48 V.
Accordingly when relay 31 operates, -48 V and ground are extended
through the tip and ring leads respectively to the PABX, in place
of the same potential applied at the central office once the trunk
has been seized.
The make contacts of contact 31B are also connected through
isolation capacitor 34 to the input of a buffer amplifier circuit
35, the output of which is connected to the input of speech
recognition circuit 36. The output of speech recognition circuit 36
is connected to data bus leads D.sub.0 -D.sub.3.
Data bus leads D.sub.0 -D.sub.3 are connected to the input of
binary decoder 42. Other outputs of decoder 42 are connected to a
receiver enable driver 46, the outputs of which are connected to
the enable inputs of a plurality of multifrequency tone receivers
(not shown) on leads RX1, RX2, RX3, RX4 etc. Driver 46 is adapted
to select on idle receiver. Multifrequency dialed digit tones are
received from the PABX portion of the trunk via operational
amplifier 47 which has its inputs connected via capacitors 48A and
48B respectively in series with resistors 49A and 49B to the PT and
PR leads. The output of operational amplifier 47 is connected
through capacitor 50 bypassed by resistor 51 to ground, to the tone
input of driver 46.
One of the selected (or a dedicated) receiver-decoders 52 is
connected as shown to the trunk leads PT and PR. The outputs of
receiver and decoder 52, which are four leads carrying well known
and standard dialing M.F. high tone frequencies, H1, H2, H3 and H4,
and four leads carrying the corresponding well known and standard
low tone frequencies, L1, L2, L3 and L4 are connected to encoder
53. The outputs of encoder 53 are connected via buffer amplifiers
54A, 54B, 54C and 54D respectively to data bus leads D0-D3. A
circuit which provides these functions is as described in Canadian
patent application entitled Tone Decoder, invented by Patrick R.
BEIRNE and Michael C. J. COWPLAND, Serial No. 312,903, filed Oct.
6, 1978. However other receivers and decoders can be used.
The break contacts of contacts 31A and 31B are connected to the
transfer contacts of relay contacts 55A and 55B. The latter
contacts provide the main trunk splitting function. Their make
contacts can be connected to a diversion trunk (labelled DIVT and
DIVR) if desired, for application of a diversion tone, a recorded
announcement, etc.
The break contacts of contacts 55A and 55B are connected to the
transfer contacts of a further set of contacts 56A and 56B. The
latter break contacts are connected to the portion of the trunk
leading to the central office, labelled as leads COT and COR. The
make contacts are connected to a termination impedance 57, which is
preferably optocoupler controlled as will be described below (but
which can be reed relay or otherwise controlled), and contains the
sensing phototransistor or photodiode (not shown) of the
optocoupler.
An additional output of decoder 42 is connected via resistor 58 to
the base of the optocoupler driver transistor 59. The emitter of
this transistor is connected through bias resistor 60 to ground,
and the collector is connected through resistor 61 to one terminal
of light emitting diode 62 of the optocoupler, the other terminal
of which is connected to a source of potential +V. Light emitting
diode 62 is coupled to the phototransistor or photodiode referred
to above used in terminating impedance 57 to form the
optocoupler.
A bridge rectifier comprising diodes 63A, 63B, 63C and 63D is
connected across the central office portion of the trunk, leads COT
and COR. The termination impedance is connected across the bridge
rectifier, deriving power therefrom; it is preferred that the
terminating impedance should be active. The terminating impedance
is enabled by means of the aforenoted optocoupler.
The make contacts of contacts 56A and 56B are connected across
impedance 57.
A decoder 64 has its inputs connected to bus leads D4, D5, D6 and
D7, and to the write enable lead of the microprocessor. Its outputs
are connected respectively to relay driver circuits 65, 66 and 67.
As an example of the relay driver circuit, driver 65 is shown in
detail.
An output of decoder 64 is connected to the junction of two of the
three series connected resistors 68, 69 and 70 connected between
sources of potential +V and -V. The junction between resistors 69
and 70 are connected to the base of transistor 71, which has its
emitter connected to ground. The collector of transistor 71 is
connected through relay coil 31C to source of potential -48 V. A
protective diode 72 is connected across relay coil 31C. As was
noted earlier, relay coil 31C operates contacts 31A and 31B.
A similar relay coil in relay driver 66 operates contacts 55A and
55B, and a similar relay coil in driver 67 operates contacts 56A
and 56B.
Also connected to the trunk tip and ring leads PT and PR are a line
voltage detector and a ringing voltage detector, and, if desired, a
line voltage polarity detector. These detectors are connected to
the tip and ring leads PT and PR through a buffer amplifier circuit
73 which has its inputs respectively D.C. coupled to these tip and
ring leads through resistors 74 and 75 in series, and 76 and 77 in
series. The junction between resistors 74 and 75 is bypassed to
ground by capacitor 78, and the junction between resistors 76 and
77 is bypassed to ground by capacitor 79.
The output of operational amplifier 73 is connected to the line
voltage detector, in particular to the non-inverting input of
operational amplifier 80 and the inverting input of operational
amplifier 81. The inverting input of operational amplifier 80 is
connected to the junction of a pair of series connected resistors
82 and 83 which are connected between a source of potential +V and
a source of reference potential K. The inverting input of
operational amplifier 81 is connected to the junction of a pair of
series connected resistors 84 and 85 which are connected between a
source of potential -V and reference potential K.
The outputs of operational amplifiers 80 and 81 are connected
together through buffer diodes 86 and 87. Their junction is
connected through resistor 88 to the base of transistor 89 which
has its emitter connected to ground (its emitter-base junction
bypassed by biasing resistor 90) and which has its collector
connected to a source of potential +V through resistor 91. Its
collector is connected through buffer 92 to data bus lead D2.
The output of operational amplifier 73 is also connected to a
ringing voltage detector through coupling capacitor 93. This
capacitor is connected through a further coupling capacitor 94 to
the non-inverting input of operational amplifier 95 and to the
inverting input of operational amplifier 96. The inverting input of
operational amplifier 95 is connected to the junction of a pair of
series connected resistors 97 and 98 which is connected between a
source of potential +V and a reference potential K. Similarly the
non-inverting input of operational amplifier 96 is connected to the
junction of series connected resistors 99 and 100, which circuit is
connected between the source of potential -V and reference
potential K. The non-inverting input of operational amplifier 95
and the inverting input of operational amplifier 96 are connected
to the reference potential K via resistor 101. The junction between
capacitors 93 and 94 is connected to source of potential -V through
resistor 102.
The output of operational amplifiers 95 and 96 are connected
together through buffer diodes 103 and 104, and their junction is
connected to the base of transistor 105 through resistor 106. The
emitter of transistor 105 is connected to ground, and the base is
connected to the emitter through biasing resistor 107. Its
collector is connected to source of potential +V through resistor
108, and to data bus lead D3 through buffer 109.
The polarity detector is also connected to the output of
operational amplifier 73, via a direct connection to the
non-inverting input of operational amplifier 110. Its inverting
input is connected to the junction of a pair of series connected
resistors 111 and 112 which are connected between a source of
potential +V and reference potential point K. The output of
operational amplifier 110 is connected through diode 113 in series
with resistor 114 to the base of transistor 115. The emitter of
transistor 115 is connected to ground, and its base is connected to
its emitter through resistor 116. Its collector is connected to
source of potential +V through resistor 117 and to data bus D4
through buffer 118.
To obtain an indication that the central office has in fact
responded to the seizure of the trunk from the PABX, a dial tone
detector, for detecting dial tone extended back to the PBX from the
central office, is also connected to the central office portion of
the trunk, and is shown in FIG. 3. If required, a loop to ground
start interface circuit should be used, as described in Canadian
patent application Serial No. 324,426 filed Mar. 29, 1978, entitled
LOOP TO GROUND START CIRCUIT, invented by Brian PASCAS, or some
other known loop to ground interface circuit.
The central office portion of the trunk, leads COT and COR are
connected via isolation capacitors 121 and 122 respectively in
series with resistors 123 and 124 to the inputs of operational
amplifier 125. The inverting input is connected via resistor 126 to
a source of balancing potential L. The output of operational
amplifier 125 is connected to the input of a CMOS switch 127.
A pair of outputs A--A of decoder 42 (FIG. 2) is connected to
corresponding inputs of inverting AND gate 128. The output of AND
gate 128 is connected through resistor 129 to the emitter of
transistor 130, the base of which is connected through resistor 131
to ground. The collector of transistor 130 is connected to the
enable input of CMOS switch 127, and through resistor 132 to source
of potential -V.
The output of switch 127 is connected through a buffer 133 to the
input of a dial tone bandpass filter 134. The output of filter 134
is connected through a threshold detector 135 in series with a
buffer 136 to data bus lead D5. Buffer 133, filter 134, and
threshold detector 136 are all of conventional construction; a
reference potential L for establishing the threshold level is
connected to threshold detector 135.
Operation of the circuit will now be described. Reference is made
to FIGS. 2a, 2b and 3 together. The microprocessor and memory
referred to is that described earlier with reference to FIG. 1.
When a subscriber goes off-hook, and accesses a trunk to the
central office, the trunk is seized in the normal manner. Line
current appears from the central office on the PT and PR leads,
which is detected in the D.C. line current detectors 30. High level
signals are placed on the data bus leads D0 and D1 via inverters
32A and 32B. These signals are received by the microprocessor,
generating an interrupt.
The microprocessor in response applies a signal to data bus leads
D0-D3, which is decoded in decoder 42, addressed to transistor 59.
As a result the LED 62 operates in the optocoupler connected in
impedance 57. The impedance provides a shunt across the COT and COR
leads, maintaining the central office portion of the trunk seized
from the point of view of the central office.
The microprocessor also applies a signal to data bus leads D4-D7
which is addressed to operate relay coil 31C. The signal is decoded
in decoder 64, and a resulting low level voltage is applied to the
junction between resistor 68 and 69 when a write signal from the
microprocessor appears on the write lead of decoder 64. As a
result, transistor 71 conducts, operating relay coil 31C. Contacts
31A and 31B operate, maintaining -48 volts and ground on the PR and
PT leads (which was previously extended from the central office
upon seizure of the trunk), and also connecting buffer amplifier 35
and speech recognition circuit 36 to the PR lead.
The microprocessor next applies a signal to data bus leads D0-D3
addressed to speech recognition circuit 36. Decoder 42 decodes the
signal, applies it to the speech recognition circuit via lead B
whereby it is enabled. The subscriber, having dialed an outside
trunk and hearing a "click" designating that the trunk has been
seized and split, now enunciates a predetermined word. The specific
word which is chosen is alternative. The word can be the calling
party's name, or a common word or words such as "line", "line
please", a number, or the like. The resulting audio signal as
passed down the PR lead, through capacitor 34, buffer amplifier 35,
into speech recognition circuit 36. The speech recognition circuit
can be the type which either identifies or analyzes the speech
patterns of the calling party, and provides an output signal on
data bus leads D0-D3 which either designates "caller identified",
or is a plurality of bits which correspond to, or are unique to the
calling party and the password.
The speech recognition circuit can be any of a number which are
current commercially available, such as the Heuristics model 7000,
or other models performing similar functions, such as model S-100,
S-2000, etc., systems such as those described in U.S. Pat. Nos.
4,227,177 issued Oct. 7, 1980 to DIALOG SYSTEMS INC., 4,227,176
issued Oct. 7, 1980 to DIALOG SYSTEMS INC., and 4,227,046 issued to
HITACHI LTD, to Vet 1 or Vet 2 terminal from Scott Instruments
Corp., etc.
It should be noted that the system is not restricted to recognition
and determination of the voice of a particular person, but may be
set up to recognize the enunciation of the words themselves, only
certain of the subscribers thus having the "password" to obtain the
class of service for outgoing calls. However, where the speech
recognition circuit is programmed to recognize individual callers
voices, separate classes of service can be allocated to each
subscriber. The recognition of one of a plurality of predetermined
subscriber's voices, as opposed to recognition of individual words,
is the preferred embodiment, whereby at least one class of service
can be given to all of the subscriber's whose voices are
recognized.
With the recognition of a password or a voice enunciating a
predetermined word a "recognition" data signal is applied by speech
recognition circuit 36 to data bus leads D0-D3. This signal is
received by the microprocessor via the data bus.
It should also be noted that the speech recognition circuit of this
invention can be utilized as a speech decoder, whereby encoded data
signals corresponding to whatever speech signals have been received
are applied to data bus leads D0-D3. In this case, the matching
data signal pattern is stored in the memory associated with the
microprocessor, and the microprocessor compares the signals
received from the speech recognition circuit with the matching
signal pattern in the equivalent of a look-up table in the
associated memory. The speech recognition circuit and the
associated memory look-up table are programmed in a manner
understood by persons skilled in the art who are familiar with the
aforenoted speech recognition circuits.
After a predetermined timed period or after determining that a word
has been spoken the microprocessor then shuts off the speech
recognition circuit 36 by applying a signal to data bus leads
D0-D3, which signal is decoded by decoder 42, and removes the
enable signal from speech recognition circuit 36 lead B. It also
addresses transistor 71, causing release of relay 31C, reconnecting
the break contacts 31A and 31B. The trunk conduction path thus
becomes continuous again from leads PT and PR to leads COT and COR.
Impedance 57 is also made high, controlled by a signal addressed
from the microprocessor to transistor 59. Dial tone from the
Central Office now reaches the subscriber. The subscriber then
dials in digits either by keying multifrequency tones or by
generating dial pulses. If the voice or password has been
recognized, these dialed digits are ignored by the circuit, and the
call proceeds as a normal outgoing call.
If the voice or words are not recognized, however, the dialed
digits are monitored by the circuit. When dial pulses are received,
the detectors 30 functioning as dial pulse detection circuitry in
conjunction with a line voltage detector detects the pulses and
applies them as signals to the D0, D1 and D2 data bus leads for
reception by the microprocessor.
The line voltage detector is comprised of differential amplifier
73, and a threshold circuit comprising differential amplifiers 80
and 81. The voltage threshold for line voltage detection is
established by the voltage K, which can be set at a reliable
indication level, depending on the line. Where the voltage -V is
-12 volts, and +V is +5 volts, the voltage at K can be chosen
intermediate between the two voltages for reliable indication of an
off-hook condition.
The output signals of operational amplifiers 80 and 81 are passed
through isolation diodes 86 and 87 to data bus driver transistor
89, which begins conducting. This places a low level input to
buffer 92, which applies a high voltage level signal to data bus
lead D2.
The microprocessor, having a look-up table of forbidden numbers or
sequences of numbers stored in memory associated with the password
or voice recognition data signal or with a particular data signal
corresponding to a voice which has been decoded compares the
dialled digits therewith. It should be noted that the digits can be
composed merely of the prefix "1", indicating the initiation of a
long-distance call, a sequence of digits indicating a forbidden
destination, a total number of digits which number indicates
desired access to a forbidden destination or trunk, etc. Upon
finding a match in its look-up table, the microprocessor addresses
a relay which operates contacts 55A and 55B, by applying an address
signal to data bus D4-D7, which is decoded in decoder 64, and as
described earlier with respect to relay driver 65, causes operation
of the relay in relay driver 66 circuit which operates trunk
splitting contacts 55A and 55B, splitting the trunk. Impedance 57
is not now activated. If a normal local interoffice call is being
made, the dialed digits merely activate the local central office,
which puts through the call. The trunk is not split.
The trunk being split causes the PT and PR leads to be connected to
the DIVT and DIVR diversion leads. If desired a tone source can be
connected to these leads, or a prerecorded message or the like
which indicates to the calling subscriber that the trunk has been
split and that his call will not be put through.
Relay contacts 55A and 55B are held operated as long as the trunk
remains seized. Should the trunk be released, this is detected by
the line voltage detector, which changes its signal applied to the
D2 data bus lead, resulting in the microprocessor causing release
of the relay operating contacts 55A and 55B.
It should be noted that when the trunk is initially seized at the
PABX, it is desirable to indicated to the microprocessor that the
central office has in fact responded to the seizure of the trunk.
While the extension of -48 volts and ground on the trunk can be
used as an indicator, dial tone is a better indicator, since it
signals that the central office is prepared to accept dialled
digits. It is preferred that operation of contacts 31A and 31B
should not occur until the dial tone from the central office has
been received.
In the dial tone detector (FIG. 3) connected to the COT and COR
leads in an A.C. isolated buffer amplifier 125, which applies A.C.
signals received from the central office portion of the trunk
circuit to the present circuit. The signals are applied through
switch 127 and buffer 133 to a dial tone filter 134. Filter 134 can
be a standard filter adapted to pass dial tone frequencies.
There are of course many different kinds of signals normally
received on the central office portion of the trunk, including
voice frequency signals (some of which may be within the frequency
band of the dial tone), ringing signals, noise, etc. Therefore it
is preferred (but is not essential) to switch the dial tone
detector circuit on only after seizure of the PABX portion of the
trunk, which establishes the time after which the dial tone signal
from the central office may be present and should be detected. Once
the trunk has been seized from the PABX, the microprocessor applies
a signal on data bus leads D0-D3 which is decoded by decoder 42,
and is applied to leads A--A. This is received in inverting AND
gate 128, which applies a high level signal to the emitter of
transistor 130. This causes the collector to go to high level,
enabling switch 127, which preferably is a CMOS switch.
The dial tone on the trunk passes through switch 127, buffer 133,
filter 134, and is applied through threshold circuit 135 to buffer
136, and thence to the data bus lead D5. Buffer (tri-state gate)
136 is enabled upon reception of a signal from the microprocessor
on the LINE READ lead. Upon reception of dial tone and indication
thereof to the microprocessor, the microprocessor shuts off switch
127 by the same method described above.
There are a number of additional circuits which can be associated
with the above-described system. Examples of some are described
below, with reference to FIGS. 2a and 2b.
The central office will apply ringing voltage to the trunk for an
incoming call to the PABX; a ringing voltage detector detects the
ringing voltage on the PABX portion of the trunk. Ringing voltage
is applied from the PT and PR leads through operational amplifier
73, coupling capacitors 93 and 94 to operational amplifiers 95 and
96. The ringing detection threshold is established by the voltage
applied to lead K which is at the junction of resistors 101 and 99.
The output of operational amplifiers 95 and 96 are applied through
isolation diodes 103 and 104 to the input of data bus driver
transistor 105. This transistor operates similarly to transistor 89
described earlier, and, upon operating, applies a high level signal
to data bus lead D3.
The microprocessor thus receives an indication that a ringing
signal has been applied to the trunk. Since this only appears with
an incoming call, the later detection of seizure of the trunk upon
answering of the call by the PABX operator inhibits the
microprocessor from causing operation of relay contacts 31A and
31B, which would otherwise split the trunk and connect the voice
recognition circuit to it. Since the ringing signal precedes the
seizure of the trunk, the transmission path is allowed to remain
intact for the duration of the call.
It should be noted that contacts 56A and 56B are normally made such
that the trunk path is through to the COT and COR leads. A diode
bridge comprising diodes 63A-63B is connected across the COT and
COR leads in a polarity direction such that power is provided for
the optocoupler-operated termination impedance 57. This circuit
preferably has a phototransistor input which drives a Darlington
transistor pair output having a typically 310 ohm load. With
contacts 56A and 56B in their idle position as shown, and with the
impedance not activated, virtually no dialing or voice signals are
diverted through the diode bridge and load.
However, upon splitting of the trunk by operation of contacts 31A
and 31B after the trunk has been seized, it must be maintained
seized to the central office. Accordingly as described earlier the
microprocessor applies a signal addressed to light emitting diode
62, by applying a binary signal to data bus leads D0-D3, which is
decoded in decoder 42. The resulting signal is appied to the base
of transistor 59, which begins conducting in its emitter-collector
circuit. This causes LED 62 to conduct, illuminating it and causing
the coupled phototransistor in load 57 to begin conducting. The
load thus becomes activated, applying the aforenoted 310 ohm
resistor across the central office portion of the trunk, COT and
COR. The central office thus detects only the maintenance of a load
thereacross, and it maintains the trunk to the PABX.
Certain PABXs seize a trunk by signalling a polarity reversal. This
is detected by sensing the D.C. voltage passed through operational
amplifier 73 from the PT and PR leads, by operational amplifier
110. The resulting output signal is applied through isolation diode
113 to the base of transistor 115. As described earlier with
respect to transistor 89, the input to inverting buffer 119 goes to
low level, and a high level signal is applied to data bus lead
D4.
Upon detection of a polarity reversal, the microprocessor applies a
signal to data bus leads D4-D7 which is decoded in decoder 64, and
which operates relay driver circuit 67. A relay coil within relay
driver circuit 67 operates as described earlier with reference to
driver circuit 65, operating relay contacts 56A and 56B. This
effectively connects the PABX portion of the trunk to the diode
bridge with opposite polarity, i.e., the ring lead being connected
to the positive terminal of the bridge (the anodes of diodes 63A
and 63C) and the tip lead to the negative terminal of the bridge.
This maintains the direction of power application to the bridge,
with the polarity reversal from the PABX.
If the subscribers connected to the PABX dial using multifrequency
keyed signals, a circuit is provided to detect such multifrequency
signals. A receiver and decoder 52 (FIG. 2) is connected across the
PR and PI leads. A suitable multifrequency digit receiver and
decoder chip is available from a number of Canadian and American
manufacturers, although the preferred circuit is described in
Canadian application Ser. No. 312,903, filed Oct. 6, 1978, entitled
TONE DECODER, invented by Michael C. J. Cowpland and Patrick R.
Beirne. The output of this or similar circuits is a binary signal
representing the high tone frequency, which appears on leads H1-H4,
and a binary signal representing low tone frequency, which appears
on a plurality of leads L1-L4. These two binary signals, a pair
representing a dialled digit, are applied to data encoder 53, and
the resulting output is applied through buffers 54A-54D to data bus
D0-D3. Where there are a plurality of receivers which are used to
service a larger number of trunk splitting circuits, the
microprocessor can of course keep record of which are currently
busy. To allocate a particular idle receiver to receive digits from
the trunk, a binary word is applied by the microprocessor to
decoder 42 via data bus leads D0-D3. This signal is applied to a
receiver enable circuit 46, which applies an output signal to one
of the leads RX1-RX4, one for the enable input of each of, for
example, four receivers.
As a variation of the above circuit, the multifrequency digit
signal is applied from leads PT and PR to A.C. isolated operational
amplifier 47, which applies the resulting signal through receiver
enable circuit 46 to the selected receiver. In this case the
receiver enable circuit switches the output of operational
amplifier 47 to the selected idle receiver input which is connected
to one of the leads RX1-RX4.
The above-described circuit thus obtains identification of the
subscriber to which trunk restriction may be implemented,
determines whether in fact a restriction is applicable, facilitates
detection of a dialled destination code, and if the call should be
denied, splits the trunk and restricts further access to the
central office portion of the trunk by the calling subscriber. The
denial or access to the trunk is thus now provided to the personal
subscriber, and is not restricted to particular subscriber's
sets.
A person understanding this invention may now conceive of other
embodiments, improvements, etc., using the same or similar
principles. All are believed to be within the sphere and scope of
this invention as defined in claims appended hereto.
* * * * *